earth science

PTAA GMB Model

PTAA GMB Model is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand PTAA GMB Model rather than just read about it. In short: PTAAGMB (Precipitation-Temperature-Area-Altitude Glacier Mass Balance) Overview The PTAAGMB Model is used for calculating a glacier's mass balance, the primary indicator of its health, and plots the changes to its mass balance over time to predict its future. Developed in the mid-1990s by glaciologist Wendell Tangborn, the PTAAGMB model provides an easy and reliable alternative to the challenging task of manually me…

Key takeaways

PTAA GMB Model belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect PTAA GMB Model to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of PTAA GMB Model from memory before moving on to harder problems.

Reference excerpt

PTAAGMB (Precipitation-Temperature-Area-Altitude Glacier Mass Balance)

Overview The PTAAGMB Model is used for calculating a glacier's mass balance, the primary indicator of its health, and plots the changes to its mass balance over time to predict its future. Developed in the mid-1990s by glaciologist Wendell Tangborn, the PTAAGMB model provides an easy and reliable alternative to the challenging task of manually measuring glaciers using snow pits and ablation stakes. The PTAAGMB model only requires data from the precipitation and temperature (PT) observations from nearby low-altitude weather stations and the glacier's area-altitude (AA) distribution.

Glacier Mass Balance and Climate Change Glaciers are ultra-sensitive to minute changes in the climate and respond by changing their size and by advancing or retreating. The mass balance, or the difference between snow accumulation and snow and ice ablation, is crucial to glacier health and its survival. The Columbia Glacier in Alaska is a large tidewater glacier that began a drastic retreat in the 1970s due to climate fluctuations and began discharging large quantities of icebergs into Prince William Sound. These icebergs were responsible for a massive oil spill in 1989 when an oil tanker captain tried to avoid them and went aground.

Area-Altitude Distribution The key to the PTAAGMB model is the glacier’s area-altitude distribution, which is simply the glacier’s surface area as a function of elevation. The AA profile is a unique feature of a glacier that has been shaped by thousands of years of erosion of the bedrock underlying the glacier. Thus, the area altitude distribution has embedded within it the past climate history that has formed the glacier. The PTAAGMB model uses daily values of such balance variables as snowline altitude, zero balance altitude, glacier balance, balance flux and the accumulation area ratio are correlated throughout the ablation season using two-degree polynomial regressions to obtain the lowest fitting error. When the minimum average error (or maximum R2) is attained, the generated balances and other variables are considered to be real. A simplex optimization technique is used to determine the optimal coefficient values that are used in algorithms to convert meteorological observations to snow accumulation and snow and ice ablation.

Application to Glaciers The PTAAGMB model has been used successfully on a number of glaciers in various parts of the world: in the United States, the Alaskan glaciers Bering, Gulkana, Lemon Creek, Mendenhall, Wolverine and Wrangell Range; in Washington State, on the South Cascade Glacier; in Europe, the Austrian glaciers Hintereisferner, Kesselwanferner and Vernagt Ferner. The mass balance and runoff of Langtang Glacier in Nepal was determined with the PTAAGMB model using daily meteorological observations observed at Kathmandu. This is the only Himalayan glacier for which mass balance and runoff have been calculated.

Glacier Thickness Calculation Another feature of the PTAAGMB model is the capability to estimate glacier thickness from ice flow velocity and mass balance measurements. The average thickness of South Cascade Glacier was found to be 83 meters in 1965, based on flow velocity and balance measurements. Borehole depth measurements of the glacier made later approximately agree with this estimate.

Mass Balance, Runoff and Surge Calculation The mass balance, runoff and surges of Bering Glacier were calculated with the PTAAGMB model using weather observations at Cordova and Yakutat, Alaska. Ice volume loss measured with the PTAAGMB model agrees within 0.8% of the loss measured with the geodetic method. Runoff from Bering Glacier (derived from simulated ablation and rain) correlates with four of the glacier surges that have occurred since 1951.

Comparison of Mass Balance Methods Comparison of glacier mass balance by glaciological, hydrological and mapping methods revealed that glaciers internally store a significant amount of liquid water. Stored water in glaciers is now considered the key to understanding the disintegration of Antarctic and Greenland Ice Caps.

More Information A website with PTAAGMB results reported from 9 different glaciers, 5 of which are compared with available manual measurements, can be seen at www.ptaagmb.com.

Worked examples

Example 1 — a first encounter with PTAA GMB Model

Start with the simplest possible case. Write down what PTAA GMB Model claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to PTAA GMB Model before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about PTAA GMB Model ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of PTAA GMB Model

In research: PTAA GMB Model appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses PTAA GMB Model in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: PTAA GMB Model is common in secondary-school and first-year university syllabi. It links to neighbouring topics Effects of climate change, Glaciology, so understanding it makes those chapters shorter.
In everyday life: Look for PTAA GMB Model outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study PTAA GMB Model in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what PTAA GMB Model means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain PTAA GMB Model out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is PTAA GMB Model in simple terms?

PTAAGMB (Precipitation-Temperature-Area-Altitude Glacier Mass Balance) Overview The PTAAGMB Model is used for calculating a glacier's mass balance, the primary indicator of its health, and plots the changes to its mass balance over time to predict its future. Developed in the mid-1990s by glaciolog…

Why does PTAA GMB Model matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study PTAA GMB Model?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on PTAA GMB Model.